A vehicle headlamp, which is configured to execute a beam switching between low beam and high beam by shifting a shade, has been previously known. For example, a vehicle headlamp including a beam switching mechanism as above driven by shifting the shade is disclosed in U.S. Pat. No. 6,286,985B1.
Although the beam switching mechanism driven by shifting the shade is employed in a so-called parabola-type lamp unit in the vehicle headlamp disclosed in the above-mentioned publication, it is also possible to employ a beam switching mechanism driven by shifting the shade in the projector-type lamp unit.
However, in the projector-type lamp unit, a light source image that forms a light distribution pattern is larger than that in the parabola-type lamp unit, due to its structural features. As a result, a luminous intensity of a hot zone (area of high-intensity light) cannot be adequately enhanced at the time of high beam irradiation, when a beam switching is executed by shifting the shade.
A detailed explanation of the problem is as follows:
FIGS. 9A and 9B show a light distribution pattern formed by beam irradiation from the lamp unit when the beam switching mechanism driven by shifting the shade is employed in the projector-type lamp unit. FIG. 9(a) shows a low beam distribution pattern and FIG. 9(b) shows a high beam distribution pattern.
In the low beam distribution pattern P(L) shown in FIG. 9(a), it is preferable that the luminosity of zone A in the vicinity of a cut-off line CL in an opposite lane is suppressed to or limited below a predetermined value. This is from the perspective of glare prevention for an oncoming driver. Meanwhile, in a high beam distribution pattern P(H) shown in FIG. 9(b), it is preferable to make zone A, as a part of the hot zone (area of high-intensity light) HZ, as luminous as possible.
Thus, contradictory requirements for lighting are made with respect to zone A, between the low beam and the high beam modes. In the projector-type lamp unit in which a light source image becomes larger, it is considerably difficult to fulfill these requirements by depending only on the absence or presence of a shade to shield the light. In this case, the luminosity of the high beam hot zone in sacrificed to some extent because priority is given to prevent glare to the oncoming driver.